WO2012095572A1

WO2012095572A1 - Internal combustion engine exhaust line

Info

Publication number: WO2012095572A1
Application number: PCT/FR2011/052876
Authority: WO
Inventors: Gabriel Crehan; Christophe Charial
Original assignee: Peugeot Citroen Automobiles Sa
Priority date: 2011-01-11
Filing date: 2011-12-06
Publication date: 2012-07-19
Also published as: EP2663747B1; EP2663747A1; FR2970295A1; FR2970295B1

Abstract

The invention relates to an exhaust line (8) of an internal combustion engine (6), comprising: - a pipe (12) receiving exhaust gases, and - a particulate filter (14) impregnated: ⋅ with a first catalytic coating forming a reduction catalyst for nitrogen oxides (NOx), and ⋅ with a second catalytic coating forming a first oxidation catalyst for carbon monoxide (CO) and hydrocarbons (HC), characterized in that: - the line (8) comprises an additional filter (30), housed in the pipe (12) downstream of the particulate filter (14) and impregnated with a catalytic coating forming a second oxidation catalyst for carbon monoxide (CO) and hydrocarbons (HC), and - the additional filter (30) has an internal structure such that the additional filter creates a pressure drop which is less than the pressure drop created by the same volume of particulate filter (14) impregnated with the same quantity of the same catalytic coating.

Description

EXHAUST LINE FOR AN INTERNAL COMBUSTION ENGINE

[001] The invention relates to an exhaust line for an internal combustion engine. The invention also relates to an engine assembly comprising this exhaust line. The invention finally relates to a vehicle equipped with this set of motorization.

[002] The exhaust gases emitted by an internal combustion engine contain pollutants which it is desirable to reduce the discharge into the atmosphere. The term "polluting elements" denotes nitrogen oxides NO _x (N ₂ 0, NO and NO ₂ ), carbon monoxide (CO), unburned hydrocarbons (HC), and soot particles. In order to limit the emissions of pollutants, it is known to carry out a post-treatment of gases passing through an exhaust line of an internal combustion engine. Typically, the exhaust line of an internal combustion engine comprises:

a manifold receiving the exhaust gases from the engine,

a particle filter for retaining and burning the soot particles contained in the gases,

an oxidation catalyst for converting the carbon monoxides (CO) and hydrocarbons (HC) into carbon dioxide (CO ₂ ) and water (H ₂ O), and - a reduction catalyst for converting the oxides of nitrogen (NO _x ) to nitrogen (N ₂ ) and water (H ₂ O).

[003] In order to minimize the size of the exhaust line, it has been proposed by the applicant to integrate the oxidation catalyst and the reduction catalyst inside the particulate filter to form a filter with so-called "bi-catalyzed" particles.

[004] A bi-catalyzed particulate filter generally has a honeycomb structure. The filter comprises an intake face for the admission of the exhaust gas and a discharge face for exhausting the exhaust gases out of the filter. The filter comprises between the intake and discharge faces a set of adjacent channels or ducts of parallel axes between they are separated by porous filtration walls. The ducts are closed at one or the other of their ends to delimit intake ducts opening only on the intake face and exhaust ducts opening only on the discharge face. The conduits are alternately closed in an order such that the exhaust gases, during the crossing of the filter, are forced to pass through the side walls of the inlet ducts to join the outlet ducts. In this way, soot particles settle and accumulate on the porous walls of the filter. These inner walls of the particulate filter are impregnated with catalytic coatings to form the reduction catalyst and the oxidation catalyst.

[005] Typically, the particulate filter is made of silicon carbide.

[006] A first disadvantage of such a type of bi-catalyzed particulate filter is that to ensure a regulatory clean-up of the exhaust gas, it is necessary that the amount of catalytic coating impregnated on the walls is greater than a minimum threshold .

If the amount of catalytic coating impregnated on the walls is too large, the pores of the filter are clogged. In this case, during operation of the engine, the exhaust gases pass through this filter more difficult. As a result, the pressure of the exhaust gas in the manifold at the inlet of the particulate filter increases. Indirectly, a clogging of the pores leads to an increase in the fuel consumption of the engine.

A known solution is to increase the volume of the particulate filter so as to deposit more catalytic coating without clogging the pores of the filter. However, this solution should be avoided because it increases the size of the exhaust line and the pressure drops in the tubing.

A second disadvantage is that to allow the reduction of nitrogen oxides (NO _x ) in the particulate filter, a reducing agent, typically ammonia, is injected into the tubing upstream of the filter. When the reducing agent passes through the filter, the agent is partially converted during the reduction of nitrogen oxides (NO _x ), and partially entrapped in the porous walls of the particulate filter. The oxidation of carbon monoxides (CO) and hydrocarbons (HC) is slow. Also, this requires a quantity of catalytic coating forming the important oxidation catalyst. If the catalytic coating forming the oxidation catalyst is present in too large a quantity in the particulate filter in the vicinity of the entrapped reducing agent (NH ₃ ), this reducing agent (NH ₃ ) is oxidized and then forms oxides. toxic nitrogen (NO _x ). These emissions must be limited.

[0010] Finally, a third disadvantage is that the bi-catalyzed filters known to the applicant are not able to reduce the nitrous oxides (NO ₂ ) at low temperature. Indeed, it takes a certain time before the particulate filter reaches a threshold temperature for this reduction. Thus, when the internal combustion engine is started up, as long as the bi-catalyzed particulate filter has not reached the threshold temperature, a large quantity of nitrous oxides (NO ₂ ) is not transformed. and is thus rejected by the exhaust line into the atmosphere.

[001 1] The invention aims to solve one or more of these disadvantages.

The invention relates to an exhaust line of an internal combustion engine, this exhaust line comprising:

a manifold receiving exhaust gases, and

a particle filter housed inside this impregnated tubing:

A first catalytic coating forming a catalyst for reducing nitrogen oxides (NO _x ), and O · a second catalytic coating forming a first catalyst for the oxidation of carbon monoxide (CO) and hydrocarbons (HC),

the line comprises an additional filter, housed in the pipe downstream of the particulate filter, impregnated with a catalytic coating forming a second oxidation catalyst for carbon monoxides (CO) and hydrocarbons (HC), and

The additional filter 51 has an internal structure such that the additional filter creates a pressure drop less than the pressure drop created by the same volume of particulate filter impregnated with the same amount of the same catalytic coating.

In the exhaust line presented above, the additional filter is capable of being impregnated with a catalytic coating amount per unit of volume greater than the particulate filter. So, to increase the amount of catalytic coating in the exhaust line, while not blocking the pores of the particulate filter, it is less cumbersome to add an additional filter to the exhaust line than to lengthen the particulate filter.

Furthermore, the additional filter creates a pressure drop less than the pressure drop that would be created by the same volume of particulate filter impregnated with the same amount of catalytic coating as the additional filter. Thus, the engine consumption is not deteriorated compared to a particle filter whose length would be lengthened.

The embodiments of this exhaust line may include one or more of the following features:

■ exhaust line, in which:

the particle filter comprises:

^* intake ducts opening only on an intake side of the exhaust gas,

* the exhaust ducts opening only on an exhaust exhaust face, and

^* Porous walls to fluidly connect the inlet ducts and exhaust ducts,

the additional filter comprises ducts opening on an inlet face on the one hand and on a discharge face on the other hand, the diameter of these ducts being greater than the pore diameter of the porous walls of the particulate filter,

The catalytic coating with which the additional filter is impregnated comprises alkali metals or alkaline earth metals, so that the filter is capable of reducing the nitrogen oxides (NO ₂ ) contained in the monoxide exhaust gas; nitrogen (NO),

The additional filter is smaller than the heat capacity of the material in which the particulate filter is made,

The additional filter is made of cordierite and / or the particulate filter is made of silicon carbide, ■ exhaust line, in which:

the intake ducts of the particulate filter are only impregnated with the first catalytic coating,

particle filter exhaust ducts are only impregnated with the second catalytic coating, and

the ratio between the volume of the first catalytic coating and the volume of the second catalytic coating in the particulate filter is greater than or equal to one, preferably greater than or equal to two.

The embodiments of this exhaust line further have the following advantages:

When the diameter of the ducts of the additional filter is greater than the pore diameter of the particulate filter, it is possible to impregnate the additional filter with a larger amount of catalytic coating per unit of volume than the particulate filter by creating a lower pressure drop,

When the specific thermal capacity of the additional filter is lower than the specific heat capacity of the particulate filter, the additional filter rises more rapidly than the particulate filter, which makes it possible to start the oxidation of carbon monoxides (CO) and hydrocarbons (HC) at low temperature when starting the engine,

When the catalytic coating of the additional filter comprises alkali metals or alkaline earth metals, the additional filter is able to reduce the nitrogen oxides (NO ₂ ) contained in the exhaust gases to nitrogen monoxide (NO) , and

When the ratio in the particulate filter between the volume of the first catalytic coating and the volume of the second catalytic coating is greater than or equal to 1, the amount of reducing agent oxidized by the second coating is limited. The invention also relates to an engine assembly, this assembly comprising:

an internal combustion engine, and

an exhaust line as presented above.

The invention finally relates to a motor vehicle equipped with this set of motorization.

Other features and advantages of the invention will become apparent from the description which is given below, for information only and in no way limitative, with reference to Figure 1. Figure 1 is a partial schematic illustration of a vehicle equipped with a motor assembly comprising an exhaust line.

In the following description, the features and functions well known to those skilled in the art are not described in detail.

[0021] Figure 1 shows a vehicle 2 such as a motor vehicle. For example, the vehicle 2 is a car. This vehicle 2 is equipped with an engine assembly 4. This assembly 4 comprises an internal combustion engine 6 and an exhaust line 8.

The motor 6 is adapted to rotate the drive wheels 10 of the vehicle 2. Here, the engine 6 is a diesel engine. During its operation, the engine 6 rejects exhaust gases that before being expelled to the outside of the vehicle 2 are received by the exhaust line 8 suitable for treating these gases.

The exhaust line 8 comprises a pipe 12 receiving the exhaust gas through an orifice 13 of an exhaust manifold of the engine 6. For example, the pipe 12 is a cylindrical tube of circular section. Here, the tubing 12 is made of steel.

The exhaust line 8 comprises a particulate filter 14

(Also called FAP) able to retain soot particles contained in the exhaust and burn these particles. Preferably, the filter 14 is capable of retaining particles of diameter greater than or equal to 23 nm. The filter 14 is disposed inside the tubing 12. The filter 14 is advantageously made of silicon carbide. The filter 14 here comprises a honeycomb structure. In this example, the internal structure of the filter 14 is known per se. Here, it has already been introduced in the introduction, so it is not described in detail. Subsequently, references 16 and 18, respectively, designate the intake face and the evacuation face of this filter 14.

The filter 14 comprises intake and exhaust ducts. In order to simplify FIG. 1, only an intake duct 20 opening on the admission face 16 and an evacuation duct 22 opening on the evacuation face 18 are represented. In the example, the ducts 20 and 22 are glued to each other by means of a cement. Typically, this cement may comprise one or more of the following chemical species: cordierite, SiC, B ₄ C, Si ₃ N ₄ , BN, AlN, ZrO ₂ , mullite, AL titanate, ZrB ₂ , and / or Sialon (alloy of silicon, aluminum, oxygen, nitride).

In the example, the length of the filter 14 is in 5cm and 75cm. Preferably the length is between 18cm and 25cm.

The filter 14 is a bi-catalyzed filter. For this purpose, the porous walls of the ducts are impregnated with two catalytic coatings.

The porous walls of the inlet ducts 20 are here only impregnated with a catalytic coating R _ca ti - The coating R _ca ti forms a selective reduction catalyst (also called SCR). This selective reduction catalyst is capable of converting the oxides of nitrogen (NO _x ) contained in the exhaust gas passing through the filter 14 into nitrogen (N ₂ ) and water (H ₂ O). The catalytic coating R _ca ti is known per se. In the example, the coating R _ca ti comprises one or more of the following chemical species: Al ₂ 0 ₃ , Ti0 ₂ , Zr0 ₂ , Ce0 ₂ , Y ₂ 0 ₃ , Pr0 ₂ , Si0 ₂ .

The porous walls of the exhaust ducts 22 are here only impregnated with a catalytic coating R _ca t2- The coating R _ca t2 forms a diesel oxidation catalyst (also called DOC). This diesel oxidation catalyst is capable of converting the carbon monoxides (CO) and hydrocarbons (HC) contained in the exhaust gases passing through the filter 14 into carbon dioxide (CO ₂ ) and water (H ₂ O). . The catalytic coating R _ca t2 is known per se. By example, R _ca t2 coating comprises one or more of the following chemical species: Al ₂ 0 _3, Ti0 _2, Zr0 _2, Ce0 _2, Y ₂ 0 _3.

The coatings R _ca ti and R _ca t2 further comprise a catalyst.

In the example, the catalyst is a material or alloy of materials belonging to the platinum group (also called "Metal Platinum Group (MGP)). By "platinum group materials" is meant here rhodium (Rh), ruthenium (Ru), iridium (Ir), rhenium (Re), osmium (Os), platinum (Pt) and palladium (Pd). Here, the catalyst is an alloy of platinum (Pt) and palladium (Pd). Still in this example, the ratio between the mass of platinum and the mass of palladium contained in the coating R _ca t2 is between 1.5 and 2.5. By way of example, this ratio is here equal to 2.

[0032] Preferably, the mass of materials belonging to the platinum group is greater in the catalytic coating R _cat2 than in the catalytic coating R _ca ti -

Advantageously, the total amount of catalyst coatings impregnated in the filter 14 is greater than or equal to 50g per liter of filter, and preferably, the total amount of impregnated catalyst coatings is greater than 100g per liter of filter. Generally, the amount of catalytic coating in the filter 14 is less than 200 g per liter of filter.

Still advantageously, the ratio between the coating volume R _cat i and the catalytic coating volume R _cat2 in the particulate filter 14 is greater than or equal to two and preferably greater than one. Right here; the ratio is greater than or equal to two. In this example, the coating R _ca ti and R _ca t2 represent respectively 70% and 30% of the total volume of catalytic coating impregnated in the filter 14.

[0035] The exhaust line 8 further comprises a reservoir 26. The reservoir 26 contains a reducing agent for reducing nitrogen oxides (NO _x) contained in the nitrogen exhaust gas (N ₂₎ and water (H ₂ O). Typically, this reducing agent is urea. Under the effect of heat, the urea is decomposed into ammonia (NH ₃₎ reacts with NO _x in the NO _x reduction catalysts coatings. The reducing agent is injected into the pipe 12 upstream of the particulate filter 14 via an injector 28. In the example, the injector 28 injects the urea downstream of a turbo-compressor ( not shown). always in the example, the injector 28 comprises an exhaust gas temperature sensor upstream of the particulate filter 14.

In this description, the terms "downstream" and "upstream" are defined relative to the flow direction of the exhaust gas in the manifold 12. The flow direction of the exhaust gas in the manifold 12 is represented by arrows in Figure 1.

The exhaust line 8 also includes an additional filter

30. The filter 30 is able to carry out the oxidation of carbon monoxides (CO) and residual hydrocarbons (HC). "Carbon monoxides (CO) and residual hydrocarbons (HC)" means carbon monoxides (CO) and hydrocarbons (HC) not converted to water (H ₂ O) and carbon dioxide (CO ₂ ) by filter 14.

The filter 30 comprises conduits 33 passing through the filter 30 from one side to the other. The conduits 33 open on an inlet face 32 on the one hand and on a discharge face 34 on the other. In order to simplify FIG. 1, only two ducts 33 are shown. The ducts 33 are separated by internal walls 35. Here, these walls 35 are less porous than the internal walls of the filter 14.

The inner walls 35 of the filter 30 separating the conduits 33 between them are impregnated with a catalytic coating R _ca t3 forming an oxidation catalyst. In the example, the coatings R _ca t2 and R _ca t3 have the same chemical composition, except that the coating R _ca t3 comprises alkali metals and / or alkaline earth metals so as to be able to reduce the dioxides. nitrogen (NO ₂ ) not reduced by the low temperature nitrogen oxide (NO) particulate filter 14.

Moreover, again in the example, in the coating R _ca t3, the ratio between the mass of platinum and the mass of palladium is advantageously between 0.2 and 1. Here, this ratio is equal to 0.5.

The filter 30 is housed in the tubing 12 downstream of the particulate filter

14. The distance separating the filters 14 and 30 is here less than 20 millimeters, preferably less than 10 millimeters.

In the remainder of this description, the term "mass thermal capacity of a material" means the energy that must be provided to a mass of 1 kg of this material to increase its temperature of a Kelvin. Thermal capacity is expressed in Joule. Kelvin ^"1. Kg ^{" 1} . The specific heat capacity of a material defines the ability of this material to absorb heat and to restore that heat.

Advantageously, the thermal capacity of the material in which the filter 30 is made is less than the heat capacity of the material in which the filter 14 is made. Under these conditions, during operation of the engine 6, the temperature inside The filter 30 achieves the "light-off" temperature faster than the filter 14. By "light-off" temperature, the temperature at which 50% of the carbon monoxide (CO) and hydrocarbons ( HC) contained in the exhaust gas are oxidized by the oxidation catalyst coating. Under these conditions, the oxidation of the carbon monoxides (CO) and hydrocarbons (HC) is implemented more rapidly in the filter 30 than in the filter 14, which allows the exhaust gases to be cleaned up earlier in the process. starting the engine 6.

Moreover, in order to allow the filter 30 to increase temperature quickly, the length of the filter 30 is preferably between 2cm and 10cm, and preferably between 5cm and 10cm.

Finally, the filter internal structure 30 is chosen so that, at equal volume with the filter 14, the filter 30 is capable of being impregnated with a quantity of coating R _C at3 per unit of volume greater than the filter 14, while by creating a lower pressure drop. Thus, the internal structure of the filter 30 is such that the pressure drop it creates is less than the pressure drop that would be created by the particle filter 14 of the same volume and impregnated with the same amount of the same coating. For this purpose, in the example, the diameter of the ducts 33 is greater than the pore diameter of the internal walls of the particulate filter 14.

Indeed, the conduits 33 passing through the filter from one side to the other and the wall

35 being low porosity, the pressure drop generated by the filter 30 is a function of the length of the filter 30, the amount of coating impregnated on the walls 35 and the diameter of the ducts 33. Conversely, the ducts 20 and 22 being plugged at one face of the filter 14, the pressure drop generated by the filter 14 is a function of the length of the filter 14, the amount of impregnated coating and the pore size of the porous walls.

In the example, the filter 30 is a monolith of cordierite. The exhaust line 8 further comprises sensors 36 and 38 of the amount of NO _x contained in the exhaust gas, respectively, upstream of the filter 14 and downstream of the filter 30.

The exhaust line 8 finally comprises a computing unit 40 for: · acquiring measurements from the sensors 36 and 38, and

• control the amount of urea injected by the injector 28 into the tubing 12 according to the acquired measurements.

For example, the unit 40 is made from a programmable electronic computer capable of executing instructions recorded on an information recording medium 42. For this purpose, the unit 40 is connected to a support information recording system containing instructions for executing a method of controlling the sensors 36, 38 and the injector 28.

Many other embodiments are possible.

Other materials may be used to produce the filters 14 and 30. For example, the filters 14 and 30 may comprise one or more of the following materials: Cordierite, SiC, B ₄ C, Si ₃ N ₄ , BN, AIN, Al ₂ O ₃ , ZrO ₂ , mullite, Al titanate, ZrB ₂ , and Sialon.

In coatings R _ca t2 and R _ca t3 the catalyst does not necessarily include a platinum group material. Other catalysts may be used in addition or in replacement. For example, the catalyst may be one of the following precious metals: gold (Au), and / or silver (Ar). The catalyst may also include lanthanide metals, actinide metals, transition metals, perovskites, and / or zeolites. A transition metal can be scandium (Se), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu) or zinc (Zn).

In the coating R _ca ti, the catalyst does not necessarily include a platinum group material. Other catalysts may be used in addition or in replacement. For example, the catalyst may be one of the following precious metals: gold (Au), and / or silver (Ar). The catalyst may also include transition metals, alkali metals, metals alkaline earth metals, lanthanide metals, hydrocarbon traps such as zeolites or clay, actinide metals, and / or perovskites.

The injector may be disposed upstream of the turbo-compressor.

Other reducing agents than urea may be used. The catalytic coatings R _ca t2 and R _ca t3 may be of the same chemical composition.

The sensors 36, 38 may be omitted. In this case, the unit 40 can control the injector 28 from pre-recorded formulas or tables.

The engine is not necessarily a diesel type engine. The engine can be a gasoline engine. In this case, the particulate filter can be impregnated so as to implement the functions of a three-way catalyst.

Claims

1. Exhaust line (8) for an internal combustion engine (6), this exhaust line comprising:

a manifold (12) receiving exhaust gases, and

a particulate filter (14) housed inside this impregnated tubing (12):

A first catalytic coating forming a catalyst for reducing nitrogen oxides (NO _x ), and

A second catalytic coating forming a first catalyst for the oxidation of carbon monoxides (CO) and hydrocarbons

(HC),

characterized in that

- The line (8) comprises an additional filter (30), housed in the pipe (12) downstream of the particulate filter (14), impregnated with a catalytic coating forming a second catalyst for oxidation of carbon monoxides (CO ) and hydrocarbons (HC), and

- The additional filter (30) has an internal structure such that the additional filter creates a pressure drop less than the pressure drop created by the same volume of particulate filter (14) impregnated with the same amount of the same catalytic coating.

2. Exhaust line (8) according to claim 1, wherein:

the particulate filter (14) comprises:

• intake ducts (20) opening only on an intake face (16) of the exhaust gas,

• exhaust ducts (22) opening only on an evacuation face (18) of the exhaust gas, and

Porous walls for fluidly connecting the intake ducts (20) and the exhaust ducts, the additional filter (30) comprises ducts (33) opening on an inlet face (32) on the one hand and on a discharge face (34) on the other hand, the diameter of these ducts (33) being greater than the pore diameter of the porous walls of the particulate filter (14).

Exhaust line (8) according to any one of the preceding claims, wherein the catalytic coating with which the additional filter is impregnated comprises alkali metals or alkaline earth metals, so that the filter (30) is able to reduce the nitrogen oxides (NO ₂ ) contained in the exhaust gas in nitrogen monoxide (NO).

4. Exhaust line (8) according to any one of the preceding claims, wherein the heat capacity of the material in which the additional filter (30) is produced is less than the heat capacity of the material in which the filter is made. particles (14).

5. Exhaust line (8) according to any one of the preceding claims, wherein the additional filter (30) is made of cordierite and / or the particulate filter (14) is made of silicon carbide.

6. Exhaust line (8) according to any one of the preceding claims, wherein:

the intake ducts (20) of the particulate filter (14) are only impregnated with the first catalytic coating,

exhaust ducts (22) of the particulate filter (14) are only impregnated with the second catalytic coating, and

the ratio between the volume of the first catalytic coating and the volume of the second catalytic coating in the particulate filter (14) is greater than or equal to one, preferably greater than or equal to two.

7. Motorization assembly (4), this assembly comprising:

an internal combustion engine (6), and

an exhaust line (8) according to any one of the preceding claims.

8. Assembly (4) according to claim 7, wherein the engine (6) is a diesel type engine.

Vehicle (2), characterized in that it comprises a drive assembly (4) according to claim 7 to 8.